Method for preparing photographic emulsions



Patented Oct. 11, .1949

' METHOD FOR 1 PREPARING: PHOTOGRAPIHG EMULSION S Wesley G; Lowe and Kearney P. Griffin, Rch=- ester, N. Y., assignors to Eastman Kodak Company,- Rochester, N. Y., a corporation of New:

Jersey No "Drawing. Application March 2', 1946, Serial No. 651,610

7 Claims: 1

This invention relatesto non-gelatin silver halide photographic emulsions" prepared by peptizing silver halide with poly-vinyl pyridine and subsequently. mixing the peptized silver halide with a non-gelatin protective colloid'for the silver halide.

In the preparation of silver halide photographic emulsions, itis customary t'o-prepare the-silver halide in thepresenceof 'a-peptizing or' dispersing agent toobtain a grainsiz'e finerthan that oldtained without the use of the peptizer.

In thepreparatiorr of- 'gelatino silver halide emulsionsgelatin can be conveniently employed as the peptizingagent, .the dispersion formed being readily compatible with further gelatin to form: a satisfactoryiemulsion. L Gelatin;- however, is incompatible with some of theireco'gnized non gelatin protective colloidsv for silver. halide. Hydrolyzed gelatin which is more compatible with the protective colloids suiier'sdrom the disadvan tage that when used as a peptizer for silver halide, emulsion washing causes difiusion of the-hydro lyzed gelatin and-silver Iossocc'urs: It hasbe'en found. that the use ofpolyvinyl pyridine as the peptizer for silver halides has an important advantage over that of gelatin in that polyvinyl pyridine is compatible with non-gelatin protective colloids.

One object of our invention is to provide nongelatin silver halide emulsions having the degree of speed desired. Another object of our invention is to provide a method of preparing silver halide dispersions which are readily compatible with non-gelatin protective colloids. A further object of our invention is to prepare silver halide dispersions using polyvinyl pyridine as the peptizing agent. Other objects of our invention will appear herein.

Polyvinyl pyridine may be prepared by polymerizing vinyl pyridine, such as by heating to its boiling temperature. A method of preparing polyvinyl pyridine is described in French Patent No. 849,126. The polyvinyl pyridine is dissolved in aqueous acid, such as 1-5% strength acetic acid. Instead of acetic, some other acid may be employed, such as formic, chloracetic, nitric, sulfuric, phosphoric, or the like, the polyvinyl pyridine being most useful in the form of its salt.

After the polyvinyl pyridine is dissolved, silver halide is formed in that solution by introducing a solution of silver salt and a halide into the polyvinyl pyridine solution. This is preferably accomplished by introducing the solutions of halide and silver salt into the polyvinyl pyridine solution simultaneously with agitation or stirring. This 2,: dispersion may" then be mixed directly with a solution of a non-gelatin-protectivc colloid and sensitized as desiredto forma photographic emuls1on:

The concentration of the solution of polyvinyl pyridine employed-'to-disperse the silver halide'is not critical, it only beingnecessary that suflicient be present to assure dispersionof the'silve'r halide. For instance, as little am will have'a'peptizing efiect; although aconsi'derable formation of silver halide will require more'pol'yvinyl' pyridine for best results; A 2% solution of"polyvinyl'pyridine has been found to be suitable underordinary conditions'of operation. For economic reasons, it is preferable not. to exceed a 10% concentration. The amount of acidused" need only be sufficient to combine with th polyvinyl pyridinebut alsoin this case; the proportion used. is not. particularly critical, an excess not: interfering withthe preparation of the dispersed silver halide.

As the protective colloid. or carrier for the dispersed silver. halide any. of. the non-gelatin materials foundto be useful for this purpose may be employed. The. far-hydrolyzed cellulose -estersv as d'escribed'and'claimed in Salo Patent N 0. 2,110,491, may be employed. Other materials which might be employed are (1) a polyvinyl acetaldehyde having a polyvinyl acetal content of at least 50% and a polyvinyl alcohol content of at least 15% as described and claimed in Fordyce Patent No. 2,211,323; (2) a polyvinyl propionaldehyde or butyraldehyde acetal having a -60% vinyl alcohol content in the case of the former, or a 60-80% vinyl alcohol content in the case of the latter as described and claimed in Lowe Patent No. 2,253,078; (3) polyvinyl alcohols (which is the term ordinarily used for compounds which are all polyvinyl alcohol except for (LS-5% polyvinyl acetate) the use of which in emulsions is disclosed in Lowe Patents Nos. 2,286,215 and 2,276,323, or (4) polyvinyl acetates having a polyvinyl acetate content of 59-71%, the use of which in emulsions is disclosed in the patents referred to in (3).

The following example illustrates our invention:

Example 1.--Two grams of polyvinyl pyridine were dissolved by stirring with a mixture of 300 cc. of water, 10 cc. of acetic acid and cc. of ethanol. This solution was heated to 84 F. and the following solutions A and B were run therein simultaneously with good stirring over a period of two minutes:

Solution A.-Ten grams of silver nitrate dissolved in water and made up to a total volume of 20 cc.

Solution B.-7.6 grams of potassium bromide and 0.24 gram of potassium iodide dissolved in water and made up to a total volume of 20 cc.

The silver halide formed was very fine grained. The silver halidedispersion was mixed with 100 grams of a 12% aqueous solution of polyvinyl alcohol (viscosity-22 secs). The mixture was diluted with water to the viscosity desired for smooth coating. The resulting emulsion was sensitized by adding 4 mg. 'of 2,3'-diethyl-4- methyloxathiazolocarbocyanine iodide and the coated out onto a baryta-coated paper. It is to be understood that all of the above procedures were carried out under darkened conditions to avoid deterioration of the silver halide.

The photographic paper thus prepared had a low contrast and very low speed and, therefore, could be handled safely in subdued daylight. It developed and fixed readily in the conventional developing and fixing baths.

Our invention includes the preparation of any of the silver halides (Cl, Br, or I) or their mixture. Although our invention has been described in conjunction with the use of non-gelatin pro-. tective colloids, the preparation of silver halide dispersions with polyvinyl pyridine for g'elatino silver halide photographic emulsions is also within the scope of our invention.

We claim:

l. A silver halide dispersion essentially consisting of a suspension of silver halide prepared by a double decomposition reaction in an aqueous solution of polyvinyl pyridine.

2. A method of preparing a photographic silver halide emulsion which comprises preparing silver halide by double decomposition between a watersoluble silver salt and a water-soluble halide in an aqueous solution of polyvinyl pyridine and subsequently mixing the so-prepared silver halide containing polyvinyl pyridine with a protective colloid therefor.

3. A method of preparing a photographic silver halide emulsion which comprises preparing silver halide by double decomposition between a watersoluble silver salt and a water-soluble halide in .4 an aqueous solution of polyvinyl pyridine and subsequently mixing the so-prepared silver halide containing polyvinyl pyridine with a non-gelatin protective colloid therefor.

4. A method of preparing a photographic silver halide emulsion which comprises preparing silver halide by double decomposition between a watersoluble silver salt and a water-soluble halide in an aqueous solution of polyvinyl pyridine and subsequently mixing the so-prepared silver halide containing polyvinyl pyridine with polyvinyl alcohol as the protective colloid therefor.

5. A photographic silver-halide emulsion comprising an aqueous mixture of finely dispersed silver halide, polyvinyl pyridine in which the dispersed silver halide was prepared by a double decomposition reaction, and a protective colloid for the "dispersed silver halide.

6. A photographic silver-halide emulsion comprising an aqueous mixture of finely dispersed silver halide, polyvinyl pyridine in which the dispersed silver halide was prepared by a double decomposition reaction and polyvinyl alcohol as the protective colloid for the dispersed silver halide.

7. A method of preparing a silver-halide dispersion which comprises simultaneously adding to an aqueous solution of polyvinyl pyridine aqueous solutions of silver nitrate and of alkali metal halides.

WESLEY G. LOWE. KEARNEY P. GRIFFIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,276,322 Lowe Mar. 17, 1942 2,281,703 Lowe May 5, 1942 2,322,085 Yutzy June 15, 1943 2,397,865 Jennings Apr. 2, 1946 

